The invention relates to a calibration device for a plastic extrusion system comprising a housing to receive coolant through which a plastic profile may be transported and thus cooled by the coolant, calibration guides through which the plastic profile passes, inlet and exhaust openings with connected lines for the coolant where the level of the coolant lies above the highest point of the plastic profile to be calibrated and is so adjusted that a liquid-free, air-filled volume remains above the level of the coolant, and an air exhaust opening positioned above the level through which air may be extracted and a partial vacuumPu=Pa−ΔPmay be created in the liquid-free, air-filled volume above the coolant level with respect to ambient air pressure, whereby Pu is the partial vacuum prevailing in the calibration device, Pa is the ambient air pressure prevailing outside the calibration device, and ΔP is the difference between the two pressure values, each of which is measured in height units of a coolant column.
Plastic hollow profiles pressed out of an extruder are passed through cooling baths for calibration. A partial vacuum is required for calibration of the plastic hollow profile. With such so-called full baths, the profile is passed through an immersion bath of coolant located within the housing, mostly tap water. Circulation of the coolant requires a pump with relatively high output since air and water are passed through most calibration devices.
A procedure and a calibration device are known from DE 196 22 419 in which the convection flow is maintained to be a laminar as possible, whereby the critical Reynolds index is not to be exceeded.
On the one hand, it is difficult to prevent a turbulent flow with a profile passing through with constant input and extraction of the coolant. On the other hand, it is not always simple to separate the air from the water.